1. Field of the Invention
The present invention relates to an integrated circuit mounting DRAM formed by using a thin film semiconductor film, and more particularly to a semiconductor display device (semiconductor device) comprising the integrated circuit and a driving method of the integrated circuit.
2. Description of the Related Art
Generally, a flat panel display formed by using an inexpensive glass substrate has a problem in that, the periphery of a pixel portion (frame area) which is used for mounting occupies larger area of the substrate as resolution becomes high, and this makes it difficult to produce a compact flat panel display. Therefore, it is considered that there is a limitation with regard to a method for mounting an IC which is formed by using a single crystal silicon wafer on a substrate, and thus technology for monolithically forming an integrated circuit and a pixel portion onto a glass substrate, namely development of a system-on-panel is expected to be advanced.
A configuration of a dual-gate thin film transistor which is one of the semiconductor elements formed on a glass substrate is disclosed in the following Patent Document 1.
[Patent Document 1]
Japanese Patent Laid-Open No. 2002-359376
Since an integrated circuit formed on a glass substrate has a lower degree of integration than that formed on a single crystal silicon wafer, the realization of high integration is an important subject in view of its practical use. In particular, enlargement of capacitance of a semiconductor memory is indispensable to achieve a high-performance integrated circuit as well as the high integration. Among semiconductor memories, DRAM (Dynamic Random Access Memory) is superior to other semiconductor memories in its large capacity and low cost. DRAM generally comprises a simple memory cell in which one transistor and one capacitor are arranged, and the smaller number of semiconductor elements are used to configure the DRAM memory cell as compared to other semiconductor memories such as SRAM. Therefore, the large number of memory cells can be embedded into one tip, thus makes it easier to produce an LSI having large memory capacity, leading to low cost per bit as compared to other semiconductor memories.
Thus, DRAM can be thought as one of the essential semiconductor memories in promoting high integration of an integrated circuit which is formed on a glass substrate.